Making a hole in a kiln for thermocouple

I'm in the process of finishing a DIY programmable controller box for my kiln. The kiln has the Sitter, and I'm not going to make any changes to the kiln. However, I need to install a thermocouple, so drilling a hole for it will be my next step. The kiln is an Evenheat 18"dia x 20" octagonal one. It has a stainless steel outside shell and 4"-high extension ring.

First, I thought about drilling a hole just below the Sitter cone holder. Then I decided not to attempt getting inside the control box and, instead, drill a hole in the ajacent wall. It would be easier to drill the lid, but I don't think measuring temperature on the top where it's higher is a good idea (no downdraft vent yet). Yes, I can make adjustments, but I'd rather know the actual temperature in the middle of the kiln (approx., the Sitter cone level). Besides, the lid is not covered with a metal shell, so attaching terminal plate to it will be very problematic.

Have you ever done it? What area did you choose for the thermocouple?

Did you use any refractory compound to seal around the thermocouple's insulation rings or went with just a reasonably close fit? I think sealing the space around is not a good idea since the thermocouple may need to be replaced at one point.

What are your thoughts, ideas and hints? It sounds like an easy and very straight forward procedure, but it's always better to get a second opinion.

On a skutt the thermocouple on a manual model kiln with sitter is on same plain as sitter (middle section about 10 inches from sitter tube.
Just make sure the probe is not where you have stilts (in the octo corners) in the middle section between the elements away from posts/stilts
The lid is a bad idea for many reasons
just make a small piliot drill hole -I would drill it inside out as inside matters more then ouitside- use a larger drill for final hole size.
Do not forget to enclose the thermo couple for long life with a protection tube.
Mark

Have you tried using the peep holes or are you looking for a permanent installation? The only down side I noticed is that it takes a few minutes to get a reading but you can move around to get readings in different areas.

Thank you for your suggestions. I finished the installation last night. It was really easy and uneventful. For the completeness sake (in case other people find it helpful), let me describe the procedure.

I installed my thermocouple at, roughly, the same level with the Sitter, but on the adjacent wall. My peep holes are to the left of the control box, and the thermocouple is to the right of it.

I measured the distance between the upper rim of the chamber to the midpoint of a brick, transferred the measurements outside and drilled from the outside in. Before drilling, make sure the termocouple is not going to be at the same level as your shelf when the shelf is rested on your posts. This will keep the thermocouple away from the large mass of the shelf that heats and cools slowly and may therefore affect reading.

A smaller pilot drill was followed by a 15/32" drill. As always with drilling stainless steel, you need to use slower speed and a sharp drill (preferably, with a 135 degree point) and apply definitive pressure so that the drill grabs the metal right away. If you rub the drill against stainless steel, the drill will dull, stainless steel will work harden and make further drilling much more difficult.

Then I inserted the thermocouple with a nice reasonably tight fit. A made it so that it protrudes into the chamber a healthy 1 3/4" (approximately, as much as the Sitter does). Then I tried inserting a kiln shelf to check if the thermocouple doesn't interfere with its insertion. Such a significant protrusion of the thermocouple will insure a more true temperature reading. Besides, it played well with the lengths of the thermocouple insulation rings (by the way, I needed to remove two one them to fit my wall thickness). Then I attached the thermocouple to the terminal block to mark the block holes location and took the block away. Then I drilled very small holes and re-attached the block with sheet metal screws. Finally, I cut extra protruding thermocouple wires using an angle grinder with a cutting wheel attached.

Frankiegirl,

This is a permanent installation to automatically control firing cycles. I did use peep holes for taking occasional temperature readings before though. But thank you for your suggestion anyway.

Just make sure you realize that the PID controller is just a part of the device and will require much more than a simple purchase. If you're not comfortable with schematics, soldering and PID programming, you're much better off spending money on a commercial wall mounted controller. Those PIDs are a major headache to program and reprogram. Besides, your kiln should be able to accept the device (mine required some tweaking with electronic controls).

Thanks for the advice (last month....). I finally broke down and bought a field box from AIM; I am installing today and must drill for the thermocouple. I am very eager to have a bit more temp control.....now I just have to program the thing!

I forgot to mention. Make a small indentation in the metal before you start drilling. Otherwise your drill will wonder around. If you don't have a proper tool for it (center punch. Ideally, automatic), just use a large nail. But be gentle with your hammer to prevent any damage to the underlying brick.

It would be safer if you use a smaller drill, first (from 1/8" to 1/4"), and then enlarge the hole with the final size drill. Keep it perpendicular to the surface.

What are your thoughts, ideas and hints? It sounds like an easy and very straight forward procedure, but it's always better to get a second opinion.

If your thermocouple has a metal sheath, the hole in the stainless steel case should be a little wider than the firebrick thermocouple hole. This prevents the thermocouple from shorting out against the case.

Thank you for the input, Arnold. My thermocouple doesn't have any sheathing (it's slow as hell as it is considering the size of the wires). By the way, aren't both, the sheath and the kiln shell, supposed to be grounded anyway?

Thank you for the input, Arnold. My thermocouple doesn't have any sheathing (it's slow as hell as it is considering the size of the wires). By the way, aren't both, the sheath and the kiln shell, supposed to be grounded anyway?

The kiln case is grounded. The thermocouple on the Bartlett and Orton controllers should not be grounded. A connection to ground can interfere with the accuracy of the thermocouple.